Melted forever brownies

Name: Melted forever brownies
Cuisine: American
Ingredients: 8 x 8-inch pan (preferably metal) 0; Butter for the pan; ¼ cup Dutch process cocoa powder; 5 ounces (142g) semisweet chocolate (preferably 64 to 68% cacao), coarsely chopped; 6 tablespoons unsalted butter; ¼ cup neutral oil, such as vegetable or grapeseed (2 oz / 56g); ½ cup granulated sugar (3.5 oz / 100g); ½ cup packed dark brown sugar; 1 large egg (1.8 oz / 50g); 2 large egg yolks (1.1 oz / 32g); 1½ teaspoons vanilla extract; ¾ cup all-purpose flour (3.5 oz / 100g); 2 tablespoons malted milk powder 2; 1 teaspoon Diamond Crystal kosher salt (0.11 oz / 3g); 6 ounces (170g) milk chocolate, coarsely chopped (1 cup)